The Gordon Research Conference (GRC) Host-parasite Interactions is the most prominent venue for scientific exchange at the leading edge of modern parasite research. This conference has been consistently at the forefront of the field since its inception in 1981 (originally under the title Parasitism). The conference will focus on new concepts and approaches in the study of parasites and their interaction with humans. This meeting will specifically address mechanisms of pathogenesis both from the viewpoint of parasite virulence factors and also changes in the host associated with infection. This group includes a large number of important disease causing agents with national and global impact. Among these are classical agents of tropical disease including malaria, sleeping sickness, chagas disease, leishmaniasis and amebic dysentery and numerous helminth infections. Together they claim millions of lives around the world. Parasitic disease are also highly prevalent in the U.S. including toxoplasmosis, cryptosporidiosis and trichomiasis. Trichomonas alone causes more than 7 million symptomatic infections each year in the U.S. Toxoplasma causes congenital infection. Some of these diseases are of a particular importance as opportunistic infections in AIDS and transplant patients and a number of parasites (in particular those with spore-like infectious stages) are of biodefense concern and are featured on Appendix B of the CDC/NIAID pathogen list. Numerous important challenges remain largely unmet when facing these diseases. There is currently no effective vaccine available for any human parasite and the options for drug treatment are far from satisfactory. The GRC is highly valued by the community as an opportunity to gain an overview of the entire field, to learn about the most recent and most exciting advances and to discuss and set the national and global research agenda for the future. It is also an important opportunity for trainees to foster their professiona development.